Abstract: To investigate the characteristics of the macrozoobenthos community structure and their relationship with environmental factors in the Laoguan River, a survey was conducted at eight sampling sites from November to December 2024. Hierarchical clustering, non-metric multidimensional scaling (NMDS), and redundancy analysis (RDA) were employed, along with the biological index(BI), the Biological Monitoring Working Party (BMWP) score, and the Ephemeroptera, Plecoptera, and Trichoptera (EPT) index for water quality assessment. The results showed that a total of 34 macrozoobenthos species belonging to 3 phyla were identified in the river, with Arthropoda being the dominant phylum. The spatial distribution of the community structure could be classified into three groups, which was highly consistent with the intensity of anthropogenic disturbance. The upstream Group A sampling sites (control) were dominated by sensitive taxa such as EPT, exhibiting a relatively intact community structure. The midstream and downstream sampling sites, affected by mining and urban construction, were dominated by pollution-tolerant taxa (e.g., Chironomidae, Corbicula), leading to a simplified community structure. The first two ordination axes (RDA1 and RDA2) cumulatively explained 73.5% of the variation in the macrozoobenthos community structure, indicating that environmental factors had strong explanatory power for the community structure variation, with water temperature and conductivity being the key influencing factors. The water quality in the upstream was good, but it declined significantly in the midstream and downstream, accompanied by marked degradation of the aquatic community, specifically manifested as a decrease in the abundance of sensitive aquatic insect taxa and an increase in pollution-tolerant taxa. Sampling site B3 showed a local recovery trend due to its greater distance from disturbance sources and certain self-purification capacity, but the EPT abundance remained relatively low (13.2%), reflecting slight water quality degradation. The assessment results differed among the various indices, highlighting the need for a comprehensive evaluation combining multiple indices to accurately ascertain the true status of the river water quality.

Key words: macrozoobenthos, community structure, characteristics, water quality assessment, Laoguan River